This is the Wista Groundglass/Fresnel Sandwich combination used by Wista on their 8x10 field camera, and is offered here as a replacement for a lost or damaged groundglass/fresnel.
Wista employs this unique, fused combination of traditional groundglass with fresnel lens overlay, along with a protective glass closer to the photographer in the optical path. This 'sandwich' is known for especially good brightness with a standard ~300mm lens for an 8x10 camera.
This viewing instrument may work with other 8x10 cameras, but is only specified for Wista's 8x10.
- Fused pairing of normal ground glass and fresnel lens